吾妻光良 & THE SWINGING BOPPERS
This was the first BP (Bop Session/Bop Party) at this venue, but after all, I think they're more suited to 'Shitamachi' (downtown) than 'Yamanote' (uptown) locations. But barely, if it's 'Kakkō Valley (Uguisudani)', is that considered 'Yamanote'? Okachi-san's drums are what make this group look the part, I felt again from the 5th-floor seats.
Source: Wikipedia